'Björn Baldus' via weewx-user <[email protected]> writes: > Maybe somebody can help us? Searching for an energy efficient rpi > distribution with cut down features - enough to run weewx properly. > We are running a rpi with an Davis vantage pro 2 activ solar powered > with a 12V 45ah Backup - but we need to cut down the power > consumption. After a few days without sun the battery is running low. > The Only functions that should work (so far as i know): > - rudimentary security (firewall) > - ssh console > - weewx (without generating graphics or some other crap) > - lan for the connection to the mr3020 - or a 3g dongle connected to the rpi > via usb
It has seemed to me that the RPI uses a fair bit of power always, even if not actively using the CPU. How are you going from your 45 Ah (presumanbly lead acid) battery to power the RPI? I would expect you'd want a high-efficiency buck converter. I would expect the RPI to take a bit more than 200 mA. Let's say 250 mA. So that's 1.25W, or about 100 mA at 12V. So that's 2.4 Ah/day. Assuming the Vantage takes very little, let's call that 2.5 Ah/day. So for 4 days without sun, that's 10 Ah, and that should be ok given that you should be able to use 22 Ah from your 45 Ah battery. You'll need enough panels to put 2.5 Ah into the battery in about 25-40% of the sun hours you get on a sunny day. If you get 4h on the panel on a full sun day, you should be able to get the 2.5 Ah in 1.5h (at least, if you live in New England which I'm guessing you don't!). Call that 2 Ah in 1h, and with a MPPT controller like the genasun GV-5, you'd need a 30W panel. Note also that you can get about 10% of the full sun power out of a cloudy day. So oversizing your panels a lot with a good MPPT controller is a reasonable strategy, because panels are cheaper than batteries and last longer, as long as you can mount them. Overall, my advice is to really instrument what's going on and measure the current draws and charging currents and do the math about system balance. I would expect things to be better than you describe. I have found that an RPI1 (model B still) draws a fair bit less lower than an RPI3. But maybe only 30% - I don't rememeber my measurments. -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
